Indian Institute of Technology Delhi (IITD), New Delhi, 2013
PARTICLE SIZE EFFECT FROM MICRO TO NANO ON THE THERMAL AND MECHANICAL PROPERTIES OF POLYMER COMPOSITES by: M.HOSSEIN ALAEI Department of Applied Mechanics Submitted in fulfillment of requirements of the degree of Doctor of Philosophy to the INDIAN INSTITUTE OF TECHNOLOGY DELHI JULY 2013
Certificate This is to certify that the thesis entitled, Particle Size Effect from Micro to Nano on the Thermal and Mechanical Properties of Polymer Composites submitted by Mr. Mohammad Hossein Alaei to the Indian Institute of Technology Delhi, for the fulfillment of award of the degree, Doctor of Philosophy, is a record of bonafide research work carried out by him under our supervision and guidance. This thesis has been prepared in conformity with the rules and regulations of the Indian Institute of Technology Delhi, New Delhi. The thesis, in our opinion, is worthy of consideration for award of the degree of Doctor of Philosophy in accordance with the regulations of the Institute. To the best of our knowledge, the results embodied in the thesis have not been submitted to any other University or Institute for the award of any other Degree or Diploma. (Puneet Mahajan) Professor Department of Applied Mechanics Indian Institute of Technology Delhi Hauz Khas, New Delhi-110016, India (Naresh Bhatnagar) Professor Department of Mechanical Engineering Indian Institute of Technology Delhi Hauz Khas, New Delhi-110016, India i
Acknowledgments At first I thank The God, The Almighty, for blessings for whatever I have and giving me inner solace and strength to overcome the ups and downs of life. I am very much pleased to express my gratefulness and indebtedness to my esteemed supervisors, Professor Puneet Mahajan, Applied Mechanics Department and Professor Naresh Bhatnagar, Mechanical Engineering Department of IIT Delhi, for their outstanding support during the research work. It is needless to mention that both of them have been extremely helpful to me in providing quality guidance; valuable time and of course support on various facets of the research work and other situations of life. I am extremely grateful to Prof. D. Kondo and Prof. M. Brieu for extensive help they have rendered in completion of my theoretical work. I am also thankful to my parents, my two sisters Zeinab and Niloofar and my wife Samira, who encouraged me to peruse this degree at the cost of physical and mental separation. M.HOSSEIN ALAEI ii
Abstract The recent emergence of particulate composites such as nano composites has stimulated tremendous research in material sciences and solid mechanics. Specifically, the incorporation of nano sized objects in a traditional matrix material give rise to advanced composites with improved physical properties. This is due to the fact that atoms at the surface/interface of the inhomogeneities experience a different local environment than atoms in the interior of the material and the equilibrium position and energy of these atoms will, in general, be different from those of the atoms in the interior. For a medium in which the number of atoms near the surface/interface is small compared to the total number of atoms (i.e. conventional composites), such effect is insignificant, and may be rightfully ignored. However, for a fine-scaled material and nano-inhomogeneities with a large ratio of the surface/interface region to the bulk, the surface/interface effect can be substantial. The thesis unfolds the unique experimental study of uniform shape and size spheres of silica (SiO 2 ) having a size range from 130 µm down to 15 nm in a selected polymer matrix of polypropylene to study first, the effect of particle size as a unique variable on the thermo-mechanical properties of particulate composites and secondly to identify experimentally for the first time the surface elasticity parameters using the experimental results obtained through the mechanical testing of the manufactured composite samples using Digital Image Correlation (DIC) and by inverse use of recent micromechanical models. Unlike initial assumption of surface elasticity parameters being numerical constants, it is observed that these terms are variables and are functions of particle size. Further Finite Element Method (FEM) is used to model the size-effect in the form of interphase thickness between matrix and the particle to further improve the FEM modeling of polymer composite. Experimental results obtained through uniaxial testing of prepared composite samples are correlated with the FEM results in order to find out the equivalent interface thickness of the particles of different sizes. It is observed that interface thickness is a function of particle size, which slightly increases for samples having particle size above 100 nm and exponentially for particle sizes below 100 nm. iii
Table of Contents Certificate... i Acknowledgments... ii Abstract... iii Table of Contents... iv List of Figures... vii List of Tables... xi List of Abbreviations... xii Nomenclature... xiii CHAPTER 1... 1 Introduction... 1 1.1 Composite Materials... 1 1.2 History... 1 1.3 Composite Advantages... 4 1.4 Classification of Composite Materials... 5 1.4.1 Composite Classification Based on Matrix Material... 5 1.4.2 Composite Classification Based on Reinforcement Form... 6 1.5 Heterogeneity, Homogeneity and Representative Volume Element (RVE)... 10 1.6 Modeling of Composite Materials... 11 1.7 Computational Material Modeling... 11 1.7.1 Molecular Scale Methods... 12 1.7.2 Microscale Methods... 12 1.7.3 Mesoscale and Macroscale Methods... 13 1.8 Micromechanics and Homogenization... 14 1.8.1 Eshelby... 16 1.8.2 Mori- Tanaka... 18 1.8.3 Self- Consistent... 19 1.8.4 Differential Scheme... 20 1.9 Evaluation of Existing Micro Mechanical Models for Different Cases... 20 1.9.1 Dilute Concentration (c 1~0)... 20 1.9.2 High- Concentration Asymptotes (c 1~1)... 21 1.9.3 Rigid Particles... 21 1.9.4 Voids... 21 1.10 Motivation... 22 1.11 Chapter Contents... 23 1.12 What questions will be answered by this work?... 24 CHPTER 2... 25 Literature Review... 25 2.1 Effect of Particle Size on Thermo- Mechanical Properties of Particulate Composites... 25 iv
2.1.1 Effect of Particles on Mechanical Properties of Polymer Matrix... 26 2.1.2 Effect of Particle Size on Thermal Properties of Polymer Matrix... 32 2.2 Theories for Elastic Modulus... 32 2.3 Existing Gaps and Motivation... 42 2.4 Objectives... 42 CHAPTER 3... 44 Sample Preparation... 44 3.1 Selection of Material System... 44 3.1.1 Reinforcement Particles... 44 3.1.2 Polymer Matrix... 46 3.2 Composite Compositions... 46 3.3 Dry Blending... 47 3.4 Melt Compounding... 48 3.5 Injection Molding... 49 3.6 Morphological Characterization... 49 3.6.1 Transmission Electron Microscopy (TEM)... 50 3.6.2 Scanning Electron Microscopy (SEM)... 54 3.6.3 Field Emission Scanning Electron Microscopy (FESEM)... 56 3.7 Results and Discussion... 59 CHAPTER 4... 61 Thermal Characterization... 61 4.1 DSC... 61 4.2 TGA... 62 4.3 Wide angle X- Ray scattering (WAXS)... 64 4.4 Results and Discussion... 66 4.4.1 Effect of Particle Size on Melting Behaviour of Composite... 66 4.4.2 Effect of Filler Size on Crystallization Behaviour... 68 4.4.3 Thermal Stability... 69 4.4.4 Crystallinity... 70 4.5 Conclusions... 71 CHAPTER 5... 73 Mechanical Characterization... 73 5.1 Testing for Mechanical Properties... 73 5.2 Results and Discussion... 76 5.2.1 Elastic Properties... 76 5.2.2 Ultimate Strength... 78 5.2.3 Toughness... 82 5.3 Conclusions... 83 CHAPTER 6... 84 Experimental Identification of Surface Elasticity Parameters... 84 v
6.1 Introduction... 84 6.2 Duan s Model for Prediction of Bulk and Shear Modulus of Heterogeneous Materials 84 6.3 Brisard s Model for Prediction of Bulk and Shear Modulus of Heterogeneous Materials... 89 6.4 Validation of the Observed Results with another Material System... 95 6.5 Conclusions... 97 CHAPTER 7... 98 Numerical Modeling of the Interface to Study the Size Effect... 98 7.1 Finite Element (FE) Modeling... 98 7.2 Boundary Conditions and Meshing... 99 7.3 Interface Property... 100 7.4 Determination of the Young s Modulus... 100 7.5 Results... 101 7.6 Conclusions... 103 CHAPTER 8... 105 Results, Discussion and Scope for Future Work... 105 8.1 Results... 105 8.2 Conclusions... 107 8.3 Scope for Future Work... 108 8.4 Contribution... 109 References... 110 Bio- data... 125 vi